Bourdon spring and load element



.Jam 24, 1950 w. 1. CALDWELL 2,495,314

BOURDON SPRING AND LOAD ELEMENT Filed July 16, 1947 K 2 Sheets-Sheet lINVENTOR. WILLIAM l. CALDWELL Jan., 24, 1950 W. I. CALDWELL BOURDONSPRINGl AND LOAD ELEMENT Filed July 16, 1947 2 Sheets-Sheet 2 FIG. 7

FIG. s

FIG. 9

. INVENTOR. WILLIAM l. CALDWELL BY A) ATTORNEY Patented Jan. 24, 1950 vNl 'l ED S TAT'ES NT 0F BOURBON SPRING AND-ILO-D ELEMENTl William. I.Caldwell, Rochester, N. assigner tov Taylor Instrument'Companies,RochestenN. Y., a. corporation. of New York v Application Jf'uly 16T,1947, Seriali No.4 '7.61.3284V (Cl. 7Bf-4183) 4 Claims.

This invention relates to responsive elements such as BourdonY springsandload elements.

This invention has for itspurpose a novel construction of Bourdonsprings and. load elements' which have greater reliability as well aslonger life, and also has for its purpose a novel method or" makingthem. vantages of the invention will appear from the detaileddescription and claims when taken. with the drawings in which: y

Fig. l, is a perspective View of a conventional tube system'including aBourdon spring;

Fig. 2 shows half cross-sections through a conventional Bourdon springillustrating theV usual defects therein;

Fig. 3 illustrates stepsr in the methodloi making; Bourdon springs inaccordance with the present invention;

Fig. 4. shows a partial cross-section of aBourdon spring;

Fig. 5 shows an uncoiled section of the Bourdon spring;

6 is an uncoiled section of a Bourdon spring similar to that of Fig. 5but with Wires introduced therein to. decrease the volume thereof;

Fig. 7 shows greatly enlarged one form of a theoretically idealhalf-section ofa Bourdon spring;

Figs. 8 and 9 show half sections of commercial diments of Bourdonsprings following the vachirlgs of the theoretical' form of Bourdonspring shown in Fig. 7;

Fig. l0 illustrates the invention applied to a tube system provided witha. load elementi used for measuring force or weight; and

Figs. ll and l2 illustrate sections that migh be used when the inventionis applied to load elements used for measuring pressures.

A common use of a Bourdon spring. 5 is inl a uid-i'illed tube systemwhich comprises-va. bulb t communicating throughacapillary tube l" withone end of the Bourdon spring usually made of metal.

A liquid lled tube system is generally understood to mean a measuringvtube: system that is so filled with a liquid that no vapor space existstherein in its operating range. Such tube systems are used to indicate.and record temperature, pressure, load, etc. For example, a temperaturemeasuring system might consist of a bulb. in which a temperature changecauses' a' differential volume expansionof the bulb body and the liquidtherein, which volume change is essentially' all conducted through: aconnecting` capillaryi to. at Bourdon spring. This volume change causesthe The various features and. ad-v This deilection Ina-y be compensatedforv by a, number of means including bimetalllc stripsv so'-4placedbetween the Bourdon spring take-oir arm andthe' temperaturescale,l that ambient.l tem-7 peratures: will not aiect the indica-tion.The use; of confipei-isators` generally reduces thel energy available:for overcoming friction in the instru mentV movement and. for' operatingcontrol devices. To minimize this energyiloss, Bourdonsprings arecommonly made of tubing; flattened so.` that the inner walls thereofare. very close together which makesv their internalivolum'e smallf andtherefore, the needed. compensationl is small. The cross sections of theBourdon springs used upl to.- the present time for liquid filled systemshave had small radii of. curvature at their edges with consequent highstresses that frequently led to premature. failures. of forminggenerallycaused: folds 9 (Fig. 2)v tov occur in the highly stressed'.` region,which folds increased the stress and the. tendency to; fail.,

I- have. found thaty the difficulties referred toa above can belargelyr` overcome by forming the" tubing. l0 (which eventually is made.into a Bourdon: spring) over wires Il inA such a way that one Wire is ateach inner edge' of the tubmg (Fig,A 3-)f. tubing has nearlyv the; sameradius; A (Fig. 4)@ at the edges as the radius B- of the wires used zvin. forming it. One: procedure: for forming the section is' tov draw orroll the tubingv Ill until; it-

-has a. g-ure-eightlike section. (Fig. 3cr withsuicienii spaceremaining' tol insert the` Wires IHS.. Then the tubingV isA passed'.through sets of .i rolls with. progressively wider faces that ilattenthe tubing between the wires andi.` forceslthemto:

may be used'- in the Bourdon spring toI further reduce the volume and"the need for compensa tion, as shown in Fig. 6. These Wires may Be thoseused formingv the tubing; Preferably, they' are wires of smallerd'iamel';'er than those used to form the tubing; Moreover, the" wiresAmbient. temperature.` changes Moreoventhe processi When properlyvformed, the section of the:

may be made of material having a low coeflicient of expansion such asInvar (36% nickel steel) which will further reduce the need forcompensation of the Bourdon spring.

Also, in accordance with this invention additional gain in operation andin longer life of the Bourdon spring is made possible by the use ofsections having non-uniform wall thickness as shown in the theoreticallyideal section of Fig. 7. By reducing the overall thickness of thesection, the exural rigidity of the section can be reduced.Consequently, for a given available energy, pressure change, volumechange, coil for-m, and length of tubing, reduction in the overallthickness of the section by locally reducing the thickness of thetubing, permits heavier tubing to be used which will increase thethickness of material at the edge, thereby reducing the stress there.Such sections are readily produced by passing the tubing containingwires, through rolls having the desired contour machined'in their faces.By this process it is possible to form sections having uniform strengthat the edge portion I3 (similar to a beam of uniform strength), whileleaving the central portion I 4 of the section with thick walls toproduce a large available energy, the portions I3 and I4 being connectedby a transition portion i5 located between the several pairs Aof dottedlines. ternal `radius and" section with uniform stress at the edge,together with uniformly thick walls in the'central portion of thesection, as shown in Fig. '7, appears to be the most desirabletheoretical-section.

In the modified forms of the invention illustra-ted in Figs. 8 and 9,there are disclosed sections of Bourdon springs adapted for quantityproduction.

In Fig.r 10, the invention is illustrated as applied to a load elementI8 used for measuring or controlling force, weight, or total load. Theelement comprises a straight tube which may have any of the crosssections referred to above. The passageways in the tube may be providedwith filler wires or not as in the case of Bourdon springs describedabove. The element I8 is completely sealed except that its interiorcommunicates with a capillary tube I9 which in turn communicates with aBourdon spring 20 or the like. The element I8 as well as the capillarytube I9 and the Bourdon spring 20 are lled with a suitable fillingmedium. The load may be applied to the element through anvils such as2|.

The load element illustrated in Fig. may

also beV used .to measure or control pressure. When so used, the anvils2I are not required. Often a pressure tight fitting such as a unionconnection 22 shown in dotted lines Fig. 10 would beaux'iliary equipmentwhen the element is used to measure or control pressure. When used tocontrol pressure, the element may be coiled or straight'as convenientand may have rosette sections with two, three or more lobes as shown atI8 in Fig. 11 and at I8a in Fig. 12.

I. Theterm Bourdon spring as herein used includes any tube whichfunctions by a deflection thereof, in response to differentialpressures. The Bourdon spring herein referred to may be wound -inspiral,helical or other forms as disclosed in the British patent toCowper #12,889 of 1849.-

The term load element as used'herein is a sensing element used to sensepressure, weight, or force or to sense Achanges therein.

A combination of-a relatively large in- The term responsive element isintended to be inclusive of Bourdon springs and load elements.

The term rosette refers to sections having bulbular lobes of which Fig.3c is a particular example having two lobes.

What I claim is:

1. A hollow element which changes its volume in response to theresultant or difference between pressures applied to its inner and outersurfaces, the wall of said element being continuous and in cross sectioncomprising opposed central portions having their inner surfaces closetogether, said wall also comprising marginal portions merging with saidcentral portions through transitions portions, each marginal portion atits thickest part being substantially as thick as a central portion andprogressively decreasing in thickness to its regions of merger with saidtransition portions whereby each marginal portion is essentially a beamof uniform strength, each marginal portion also dening an internalpassageway generally circular in cross section.

2. A hollow element which changes its volume in response to theresultant or diiference between pressures applied to its inner and outersurfaces, the wall of said element being continuous and in cross sectioncomprising opposed central portions having their inner surfaces closetogether, said wall also comprising marginal portions merging with saidcentral portions through transition portions, each marginal portion atits thickest part being substantially as thick as a central portion andprogressively decreasing in thickness to its regions of merger with saidtransition portions whereby each marginal portion is essentially a beamof uniform strength, each marginal portion also dening an internalpassageway generally circular in cross section, and a wire contained ineach passageway substantially filling the same.

3. A hollow element which changes its volume in response to theresultant or difference between pressures applied to its inner and outersurfaces, the wall of said element being continuous and in cross sectioncomprising opposed central portions having their inner surfaces closetogether, said wall also comprising marginal portions merging with saidcentral portions through transition portions, each marginal portion atits thickest part being substantially as thick as a central portion andprogressively decreasing in thickness to its regions of merger with saidtransition portions whereby each marginal portion is essentially a beamof uniform strength, each marginal portion also dening an internalpassageway generally circular in cross section, and a wire contained ineach passageway, the diameter of said wire being slightly smaller thanthat of the largest wire that can be inserted therein.

4. 'A hollow element which changes its volume in response to theresultant or difference between pressures applied to its inner and outersurfaces, the wall of said element being continuous and in cross sectioncomprising opposed central portions having their inner surfaces closetogether, said wall also comprising marginal portions merging with saidcentral portions through transition portions, each marginal portion atits thickest part being substantially as thick as a central portion andprogressively decreasing in thickness to its regions of merger with saidtransition portions whereby each marginal portion is essentially a beamof uniform strength, each marginal portion also dening an internalpassageway generally circular in cross section, and a wire made of amaterial having a low coelicient 5 of thermal expansion contained ineach passageway, the diameter of said wire being slightly less than thediameter of said passageway. v

WILLIAM I. CALDWELL.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Name Date Townsend Dec. 30. 1924 Number NumberNumber

